1. Technical Field
An organic anti-reflective polymer which prevents back reflection of lower film layers and eliminates standing wave that is caused by a thickness change of photoresist and light, in a process for fabricating ultrafine patterns that use photoresist for lithography by using 248 nm KrF and 193 nm ArF. More particularly, the organic anti-reflective polymer is useful for fabricating ultrafine patterns of 64M, 256M, 1G, and 4G DRAM semiconductor devices. A composition containing such organic anti-reflective polymer, an anti-reflective coating layer made therefrom and a preparation method thereof are also disclosed.
2. Description of the Background Art
In a fabrication process of ultrafine patterns for preparing semiconductor devices, standing waves and reflective notching inevitably occur due to the optical properties of lower film layer on the wafer and due to the thickness changes in the photosensitive film. In addition, there is another problem in that a CD (critical dimension) alteration is caused by diffracted and reflected light from the lower film layers. Thus, it has been suggested to introduce anti-reflective coating that prevents back reflection at a lower film layer by introducing organic material with high absorbance at a wavelength range of the light employed as a light source.
Anti-reflective coatings are classified into inorganic and organic anti-reflective coatings depending upon the material used, or into absorptive and interfering anti-reflective coatings based on the operation mechanism. For microlithography using I-line (365 nm wavelength) radiation, inorganic anti-reflective coating are predominantly used, while TiN and amorphous carbon are employed as an absorptive system and SiON are employed as an interfering system.
In a fabrication process of ultrafine patterns using KrF laser, SiON has been mainly used as an inorganic anti-reflective film. However, in the case of an inorganic anti-reflective film, no material has been known which enables the control of the interference at 193 nm, the wavelength of the light source. Thus, there has been great deal of efforts to employ an organic compound as an anti-reflective coating.
To be a good organic anti-reflective coating, the following conditions must be satisfied. First, peeling of the photoresist layer due to the dissolution in a solvent must not take place when conducting a lithographic process. In order to achieve this goal, a molded coating must be designed to form a cross-linked structure without producing any chemical by-product. Second, chemicals such as acid or amine must not come-in or go-out from the anti-reflective coating. This is because when acid migrates from anti-reflective coating, undercutting occurs at a lower part of the pattern while footing may occur when a base such as amine migrates. Third, the etching speed of the anti-reflective coating should be faster than the etching speed of the upper photosensitive film so as to facilitate etching process by using photosensitive film as a mask. Finally, the anti-reflective coating must be as thin as possible to an extent to sufficiently play a role as an anti-reflective coating.
The existing organic anti-reflective materials are mainly divided into two types: (1) polymers containing a chromophore, cross-linking agent (single molecule) that cross-link the polymers and an additive (thermally variable oxidant); and (2) polymers which can cross link themselves and contain a chromophore and an additive (thermally variable oxidant). But these two types of anti-reflective material are problematic in that the control of k value is almost impossible because the content of the chromophore is defined according to the ratio as originally designed at the time of polymerization. Thus, if it is desired to change the k value, the polymer must be resynthesized.
A novel organic polymer for anti-reflective coating and its preparation method are disclosed.
An anti-reflective coating composition comprising the aforementioned polymer and a preparation method thereof are also disclosed.
A semiconductor device on which a pattern is formed from such an anti-reflective coating by submicrolithography is also disclosed.
The following compounds having Formulas 1 and 2, respectively are provided which can be used in an anti-reflective coating. 
wherein R and Rxe2x80x2 are each independently hydrogen or methyl;
Ra to Rd, R1 to R9 are each independently xe2x80x94H, xe2x80x94OH, xe2x80x94OCOCH3, xe2x80x94COOH, xe2x80x94CH2OH, or substituted or unsubstituted, or straight or branched alkyl or alkoxy alkyl having 1 to 5 carbon atoms;
m and n each represents an integer selected from 1, 2, 3, 4 and 5;
x and y each represents mole fraction from 0.01 to 0.99;
R10 and R11 are each independently straight or branched substituted C1-10 alkoxy;
R12 is hydrogen or methyl.
The aforementioned polymer of Formula 1 is prepared from the compound of Formula 10
wherein:
R is hydrogen or methyl;
Ra Rb, and R1 to R9 are each independently xe2x80x94H, xe2x80x94OH, xe2x80x94OCOCH3, xe2x80x94COOH, xe2x80x94CH2OH, or substituted or unsubstituted, or straight or branched alkyl or alkoxy alkyl having 1 to 5 carbon atoms;
n represents an integer selected from 1, 2, 3, 4 and 5.
The above compound of Formula 10 is prepared by a condensation reaction of anthracene oxime and acrylic monomer in the presence of laurylic acid catalyst as outlined in the following Scheme 1. It is preferred that the above condensation reaction is carried out at a temperature ranging from about 30 to about 80xc2x0 C. for a time period ranging from about 3 to about 10 hours. 
The polymer of Formula 1 is prepared by reacting anthracene methyliminealkylacrylate monomer of Formula 10 with hydroxyacrylate monomer in a solvent and then polymerizing the obtained compound with a polymerization initiator. Suitable solvent is selected from the group consisting of tetrahydrofuran, toluene, methylethylketone, dioxane and mixtures thereof. As a polymerization initiator, it is preferred to use a compound selected from the group consisting of 2,2xe2x80x2-azobisisobutyronitrile, acetylperoxide, laurylperoxide, and t-butylperoxide.
The above polymerization reaction is preferably carried out at a temperature ranging from about 50 to about 90xc2x0 C. and it is preferred that the mole ratio of each monomer fall within the range of 0.01 to 0.99:0.01 to 0.99.
An anti-reflective coating composition can be characterized as containing the said polymer of Formula 1, or a composition containing both of a polymer of Formula 1 and a compound of Formula 2.
The compound of Formula 2 is prepared by polymerizing (meth)acrolein to obtain poly(meth)acrolein followed by reacting the obtained polymeric product with branched or straight substituted alkyl alcohol having 1 to 10 carbon atoms.
In detail, (meth)acrolein is first dissolved in an organic solvent and added thereto a polymerization initiator to carry out polymerization under vacuum at a temperature ranging from about 60 to about 70xc2x0 C. for a time period ranging from about 4 to about 6 hours. Then, the obtained polymeric product is reacted with branched or straight substituted alkyl alcohol having 1 to 10 carbon atoms in the presence of trifluoromethylsulfonic acid as a catalyst at a room temperature for a time period ranging from about 20 to about 30 hours.
In the above process, suitable organic solvent is selected from the group consisting of tetrahydrofuran (THF), cyclohexanone, dimethylformamide, dimethylsulfoxide, dioxane, methylethylketone, benzene, toluene, xylene and mixtures thereof. As a polymerization initiator, it can be mentioned 2,2-azobisisobutyronitrile (AIBN), benzoylperoxide, acetylperoxide, laurylperoxide, t-butylperacetate, t-butylhydroperoxide or di-t-butylperoxide. A preferred example of the said alkyl alcohol having 1 to 10 carbon atoms is ethanol or methanol.
A preferred compound of Formula 2 is selected from the group consisting of the compounds of the following Formulas 3 to 6. 
The above compounds of Formulas 3 to 6 are readily cured in the presence of acid and other polymers having alcohol group.
Further, an improved anti-reflective coating composition comprises a polymer of Formula 1, a compound of Formula 2 and an anthracene derivative as an additive. Illustrative, non-limiting examples of the anthracene derivatives (hereinafter, xe2x80x9canthracene derivative additivexe2x80x9d) is selected from the group consisting of anthracene, 9-anthracenemethanol, 9-anthracenecarbonitrile, 9-antracene carboxylic acid, ditranol, 1,2,10-anthracentriol, anthraflavonic acid, 9-anthraldehydeoxime, 9-anthraldehyde, 2-amino-7-methyl-5-oxo-5H-[1]benzo-pyrano[2,3-b]pyridine-3-carbonitrile, 1-aminoanthraquinone, anthraquinone-2-carboxylic acid, 1,5-dihydroxyanthraquinone, anthrone, 9-anthryle trifluoro-methylketone, 9-alkylanthracene derivatives of the following Formula 7, 9-carboxylanthracene derivatives of the following Formula 8, 1-carboxylanthracene derivatives of the following Formula 9, and mixtures thereof. 
wherein, R1 to R5 are xe2x80x94H, xe2x80x94OH, xe2x80x94CH2OH or substituted or unsubstituted straight or branched alkyl or alkoxyalkyl having 1 to 5 carbon atoms.
A preparation method of an organic anti-reflective coating comprises the steps of dissolving a polymer of Formula 1 and a compound of Formula 2 in an organic solvent, filtering the obtained solution alone or in combination with at least one anthracene derivatives additive as aforementioned, coating the filtrate on a lower layer and hard-baking the coated layer. More particularly, an example of the organic solvent used in this procedure includes ethyl 3-ethoxypropionate, methyl 3-methoxypropionate, cyclohexanone, and propyleneglycolmethylether acetate. It is preferred that the aforementioned solvent is used in an amount ranging from about 200 to about 5,000 wt. % based on the total weight of the anti-reflective coating polymers used. The preferred temperature range for hard-baking is from about 100 to about 300xc2x0 C.
An improved semiconductor device can be prepared from any of the aforementioned anti-reflective coating compositions.
The polymer of Formula 1 (primary polymer) is synthesized by polymerizing the monomers of Formula 10 which have large sized chromophore so that the obtained polymer of Formula 1 shows a high absorbance at the wavelength of 248 nm. In order to allow improved properties such as good molding property, air-tightness, and dissolution resistance, the compound of Formula 2 (secondary polymer), i.e., a compound capable of forming cross linkage upon the reaction with an alcohol group of the polymer during hard baking step after the coating step, is mixed with the aforementioned primary polymer to form a cross linked product.
In particular, it is possible to freely adjust the k value of the anti-reflective film by controlling the proportion of the primary polymer, because the cross linking agents used in the form of a polymer is designed to maximize the efficiency of the cross linking reaction.
Further, the anti-reflective coating resin has a good solubility in all of the hydrocarbon solvent while it will not dissolve in any of the solvents during a hard-baking step. In addition, no undercutting or footing is experienced in the fabrication process of patterns. Especially, because the anti-reflective coating resin disclosed herein is made from acrylate polymer, which enables higher etching speed relative to, that of the photosensitive film during etching process, the etching selectivity is improved with the anti-reflective coating resin disclosed herein.
The following examples are set forth to illustrate more clearly the disclosed principles and disclosed practices to a person skilled in the art. As such, they are not intended to limit the disclosure, but are illustrative of certain preferred embodiments.